Abstract: Cast TC4 alloy were welded by electron beam welding, and residual stress in matrix, heat affect zone and joint was tested by X-ray diffraction method. The results showed that there were tensile stress in joint and heat affect zone in transverse direction and longitudinal direction, where testing points were perpendicular to welding line, the shear stress values were in the scale of ±50 MPa, which had no effect on mechanical property of the joint. Testing point along the welding line, whether transverse or longitudinal stress, stress in start of welding joint was lower than which in the end of welding joint. Longitudinal stress was tensile stress, and transverse compress stress change to tensile stress gradually.